[PATCH v2] perf cs-etm: Improve completeness for kernel address space

From: Leo Yan
Date: Wed Jun 19 2019 - 21:00:02 EST

Arm and arm64 architecture reserve some memory regions prior to the
symbol '_stext' and these memory regions later will be used by device
module and BPF jit. The current code misses to consider these memory
regions thus any address in the regions will be taken as user space
mode, but perf cannot find the corresponding dso with the wrong CPU
mode so we misses to generate samples for device module and BPF
related trace data.

This patch parse the link scripts to get the memory size prior to start
address and reduce this size from 'etmq->etm->kernel_start', then can
get a fixed up kernel start address which contain memory regions for
device module and BPF. Finally, cs_etm__cpu_mode() can return right
mode for these memory regions and perf can successfully generate
samples.

The reason for parsing the link scripts is Arm architecture changes text
offset dependent on different platforms, which define multiple text
offsets in $kernel/arch/arm/Makefile. This offset is decided when build
kernel and the final value is extended in the link script, so we can
extract the used value from the link script. We use the same way to
parse arm64 link script as well. If fail to find the link script, the
pre start memory size is assumed as zero, in this case it has no any
change caused with this patch.

Below is detailed info for testing this patch:

- Build LLVM/Clang 8.0 or later version;

- Configure perf with ~/.perfconfig:

root@debian:~# cat ~/.perfconfig
# this file is auto-generated.
[llvm]
clang-path = /mnt/build/llvm-build/build/install/bin/clang
kbuild-dir = /mnt/linux-kernel/linux-cs-dev/
clang-opt = "-g"
dump-obj = true

[trace]
show_zeros = yes
show_duration = no
no_inherit = yes
show_timestamp = no
show_arg_names = no
args_alignment = 40
show_prefix = yes

- Run 'perf trace' command with eBPF event:

root@debian:~# perf trace -e string \
-e $kernel/tools/perf/examples/bpf/augmented_raw_syscalls.c

- Read eBPF program memory mapping in kernel:

root@debian:~# echo 1 > /proc/sys/net/core/bpf_jit_kallsyms
root@debian:~# cat /proc/kallsyms | grep -E "bpf_prog_.+_sys_[enter|exit]"
ffff000000086a84 t bpf_prog_f173133dc38ccf87_sys_enter [bpf]
ffff000000088618 t bpf_prog_c1bd85c092d6e4aa_sys_exit [bpf]

- Launch any program which accesses file system frequently so can hit
the system calls trace flow with eBPF event;

- Capture CoreSight trace data with filtering eBPF program:

root@debian:~# perf record -e cs_etm/@20070000.etr/ \
--filter 'filter 0xffff000000086a84/0x800' -a sleep 5s

- Annotate for symbol 'bpf_prog_f173133dc38ccf87_sys_enter':

root@debian:~# perf report
Then select 'branches' samples and press 'a' to annotate symbol
'bpf_prog_f173133dc38ccf87_sys_enter', press 'P' to print to the
bpf_prog_f173133dc38ccf87_sys_enter.annotation file:

root@debian:~# cat bpf_prog_f173133dc38ccf87_sys_enter.annotation

bpf_prog_f173133dc38ccf87_sys_enter() bpf_prog_f173133dc38ccf87_sys_enter
Event: branches

Percent int sys_enter(struct syscall_enter_args *args)
stp x29, x30, [sp, #-16]!

int key = 0;
mov x29, sp

augmented_args = bpf_map_lookup_elem(&augmented_filename_map, &key);
stp x19, x20, [sp, #-16]!

augmented_args = bpf_map_lookup_elem(&augmented_filename_map, &key);
stp x21, x22, [sp, #-16]!

stp x25, x26, [sp, #-16]!

return bpf_get_current_pid_tgid();
mov x25, sp

return bpf_get_current_pid_tgid();
mov x26, #0x0 // #0

sub sp, sp, #0x10

return bpf_map_lookup_elem(pids, &pid) != NULL;
add x19, x0, #0x0

mov x0, #0x0 // #0

mov x10, #0xfffffffffffffff8 // #-8

if (pid_filter__has(&pids_filtered, getpid()))
str w0, [x25, x10]

probe_read(&augmented_args->args, sizeof(augmented_args->args), args);
add x1, x25, #0x0

probe_read(&augmented_args->args, sizeof(augmented_args->args), args);
mov x10, #0xfffffffffffffff8 // #-8

syscall = bpf_map_lookup_elem(&syscalls, &augmented_args->args.syscall_nr);
add x1, x1, x10

syscall = bpf_map_lookup_elem(&syscalls, &augmented_args->args.syscall_nr);
mov x0, #0xffff8009ffffffff // #-140694538682369

movk x0, #0x6698, lsl #16

movk x0, #0x3e00

mov x10, #0xffffffffffff1040 // #-61376

if (syscall == NULL || !syscall->enabled)
movk x10, #0x1023, lsl #16

if (syscall == NULL || !syscall->enabled)
movk x10, #0x0, lsl #32

loop_iter_first()
3.69 â blr bpf_prog_f173133dc38ccf87_sys_enter
loop_iter_first()
add x7, x0, #0x0

loop_iter_first()
add x20, x7, #0x0

int size = probe_read_str(&augmented_filename->value, filename_len, filename_arg);
mov x0, #0x1 // #1

[...]

Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Suzuki Poulouse <suzuki.poulose@xxxxxxx>
Cc: coresight@xxxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
---
tools/perf/Makefile.config | 20 ++++++++++++++++++++
tools/perf/util/cs-etm.c | 19 ++++++++++++++++++-
2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 51dd00f65709..cf5906d667aa 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -418,6 +418,26 @@ ifdef CORESIGHT
endif
LDFLAGS += $(LIBOPENCSD_LDFLAGS)
EXTLIBS += $(OPENCSDLIBS)
+ ARM_PRE_START_SIZE := 0
+ ifeq ($(SRCARCH),arm64)
+ # Extract info from lds:
+ # . = ((((((((0xffffffffffffffff)) - (((1)) << (48)) + 1) + (0)) + (0x08000000))) + (0x08000000))) + 0x00080000;
+ # ARM_PRE_START_SIZE := (0x08000000 + 0x08000000 + 0x00080000)
+ ARM_PRE_START_SIZE := $(shell egrep ' \. \= \({8}0x[0-9a-fA-F]+\){2}' \
+ $(srctree)/arch/arm64/kernel/vmlinux.lds | \
+ sed -e 's/[(|)|.|=|+|<|;|-]//g' -e 's/ \+/ /g' -e 's/^[ \t]*//' | \
+ awk -F' ' '{print "("$$6 "+" $$7 "+" $$8")"}' 2>/dev/null)
+ endif
+ ifeq ($(SRCARCH),arm)
+ # Extract info from lds:
+ # . = ((0xC0000000)) + 0x00208000;
+ # ARM_PRE_START_SIZE := 0x00208000
+ ARM_PRE_START_SIZE := $(shell egrep ' \. \= \({2}0x[0-9a-fA-F]+\){2}' \
+ $(srctree)/arch/arm/kernel/vmlinux.lds | \
+ sed -e 's/[(|)|.|=|+|<|;|-]//g' -e 's/ \+/ /g' -e 's/^[ \t]*//' | \
+ awk -F' ' '{print "("$$2")"}' 2>/dev/null)
+ endif
+ CFLAGS += -DARM_PRE_START_SIZE="$(ARM_PRE_START_SIZE)"
$(call detected,CONFIG_LIBOPENCSD)
ifdef CSTRACE_RAW
CFLAGS += -DCS_DEBUG_RAW
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
index 0c7776b51045..5fa0be3a3904 100644
--- a/tools/perf/util/cs-etm.c
+++ b/tools/perf/util/cs-etm.c
@@ -613,10 +613,27 @@ static void cs_etm__free(struct perf_session *session)
static u8 cs_etm__cpu_mode(struct cs_etm_queue *etmq, u64 address)
{
struct machine *machine;
+ u64 fixup_kernel_start = 0;

machine = etmq->etm->machine;

- if (address >= etmq->etm->kernel_start) {
+ /*
+ * Since arm and arm64 specify some memory regions prior to
+ * 'kernel_start', kernel addresses can be less than 'kernel_start'.
+ *
+ * For arm architecture, the 16MB virtual memory space prior to
+ * 'kernel_start' is allocated to device modules, a PMD table if
+ * CONFIG_HIGHMEM is enabled and a PGD table.
+ *
+ * For arm64 architecture, the root PGD table, device module memory
+ * region and BPF jit region are prior to 'kernel_start'.
+ *
+ * To reflect the complete kernel address space, compensate these
+ * pre-defined regions for kernel start address.
+ */
+ fixup_kernel_start = etmq->etm->kernel_start - ARM_PRE_START_SIZE;
+
+ if (address >= fixup_kernel_start) {
if (machine__is_host(machine))
return PERF_RECORD_MISC_KERNEL;
else
--
2.17.1